Rescues are rewarding, but extremely difficult to deal with, regardless. I rescued Sam last year in a horrific condition, and did some light riding once his weight was at a somewhat-reasonable level. It was like riding a bucking bull that occasionally didn't buck. He has great ground manners and is completely fine with children, but has some past trauma that makes him go up, down, and sideways when an adult mounts.
Rescues are not for beginners. If you have any confidence issues what-so-ever, a rescue horse can be a dangerous, if not deadly choice. A 'bad' (problematic) rescue can even put some people off horses and riding for life. The problem is that pretty much all rescues are problematic in some way, shape or form.
If you ARE set on rescuing (I'm talking to everyone here) there are some really great rescues out there where you can sponsor and even volunteer. Help feed, muck out stalls, or even just bring a load of hay.
If are are really, really, REALLY, set on having a rescue mow your pasture then I suggest a rehabilitated horse.
A good rescue operation should WILLINGLY tell you every con in a rehabbed horse, and of course, every pro.
I myself absolutely, 100% do not regret my choice to take in Sam, despite his issues. Rescue horses are scary, and certainly more dangerous than your 'regular horse'....but I'd be a flaming liar if I'd say that seeing that skinny, scruffy horse turn into a fat retiree didn't bring me total joy.
Wait! I'll fix it....